Elevator belt assembly with prestretched cords

ABSTRACT

An elevator load bearing assembly ( 40 ) includes a plurality of synthetic or polymer cords ( 42 ) within a urethane jacket ( 44 ). The cords are prestretched and the jacket prevents the stretched cords from relaxing. The inventive arrangement provides a load bearing assembly ( 40 ) that has little or no elastic or construction stretch.

BACKGROUND OF THE INVENTION

This invention generally relates to load bearing members for use inelevator systems. More particularly, this invention relates to anelevator belt assembly having a prestretched polymer cords encased in apolyurethane material.

Elevator systems typically include a cab and counterweight that movewithin a hoistway to transport passengers or cargo to different landingswithin a building, for example. A load bearing member, such as roping ora belt typically moves over a set of sheaves and supports the load ofthe cab and counterweight. There are a variety of types of load bearingmembers used in elevator systems.

The traditional load bearing member has been a steel rope. While thisarrangement has proven useful, those skilled in the art are alwaysstriving to make improvements. Lighter weight and greater strength aretwo example load bearing assembly characteristics that are highlydesirable. Larger buildings, for example require elevators that travelgreater distances, which increases the required length of the loadbearing assembly. Lighter weight alternatives would improve theeconomies associated with elevator systems in such buildings.

While some alternative belt arrangements using lighter weight materialshave been proposed, there is a need to satisfy typical safety codes andpassenger ride quality standards. Typical codes require belts to meetselected strength criteria, and ride quality requires a minimum amountof stretch. If alternative materials were used, the design issuesassociated with meeting strength and stretch requirements potentiallybecomes more complex. Lighter weight materials may be more susceptibleto stretch and have different breaking strengths depending on thematerial composition.

This invention provides a solution to making a load bearing assembly,which has polymer material cords instead of steel, that is able tosatisfy strength and stretch requirements.

SUMMARY OF THE INVENTION

In general terms, this invention is an elevator belt assembly that hasprestretched synthetic material cords encased in a jacket that keeps thecords in a stretched condition. The inventive arrangement provides abelt assembly that has minimal elastic or construction stretch.

In one example, the cords are pre-stretched using tension that isapproximately 10% of the cord breaking strength.

A method according to this invention for making an elevator beltassembly includes aligning a plurality of synthetic material cords in aselected arrangement. Each of the cords are tensioned to pre-stretch thecords. The stretched cords are coated with a jacket so that theresulting belt assembly has cords already stretched a selected amount.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiments. The drawings thataccompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a portion of an example belt assemblydesigned according to this invention.

FIG. 2 is a cross-sectional illustration taken along the lines 2-2 inFIG. 1.

FIG. 3 is a schematic illustration of method of making a belt assemblydesigned according to an embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 schematically illustrate a portion of a belt assembly 40that is designed for use in an elevator system. A plurality of cords 42are aligned generally parallel to a longitudinal axis of the beltassembly 40. The cords 42 are prestretched a desired amount during thebelt assembly process so that the inventive arrangement provides a beltassembly that has little or no elastic stretch or construction stretchwhen the belt is subjected to operating loads once installed in anelevator system.

A flat belt assembly having rounded cords is illustrated as an examplein FIGS. 1 and 2 but this invention is not necessarily so limited. Otherload bearing assembly configurations fit within the scope of thisinvention such as roping that is not flat or an assembly that includesflat cords. The term “belt” as used in this description should not beconstrued in its strictest sense but must be understood to refer to avariety of load bearing member assembly designs.

The cords 42 preferably comprise a synthetic (most preferably a polymer)material. Example materials include PBO, which is sold under the tradename Zylon; liquid crystal polymers such as a polyester-polyarylate,which is sold under the trade name Vectran; p-type aramids such as thosesold under the trade names Kevlar, Technora and Twaron; or an ultra-highmolecular weight polyethylene, an example of which is sold under thetrade name Spectra; and nylon. Given this description, those skilled inthe art will be able to select appropriate material or combination ofmaterials to meet the needs of their particular situation.

Using a synthetic or polymer material allows for a belt having a higherstrength-to-weight ratio compared to steel coated belts, for example.

A jacket 44 covers over the cords 42. The jacket 44 preferably comprisesa polyurethane-based material that is not compressible when cured. Avariety of such materials are commercially available and known in theart to be useful for elevator belt assemblies. In one example, thepreferred urethane material is an ether based polyurethane. In aparticular example, an MDI ether based material is preferred for oneparticular embodiment of this invention.

The jacket material preferably is substantially not compressible whencured and has characteristics that render the belt assembly useful overlong periods of time within an elevator system. The frictioncharacteristics of the jacket material preferably are controlledprecisely. In one example, a friction co-efficient value of 0.2 relativeto the material of the traction sheave is the minimum preferredco-efficient. Having sufficient jacket friction characteristics ensuresproper traction during operation of the elevator system.

The jacket material preferably has a high wear resistance and isresistant to cuts or tears so that abrasion of the belt assembly doesnot readily occur over the lifetime of the assembly. It is recognizedthat abrasion to the jacket contributes to induced vibrations andpremature belt replacement and, therefore, a sufficient cut resistanceor tear resistance is desired.

An additional desired characteristic of the jacket material is to havean adequate tensile strength to carry the load between the cords 42 andthe sheaves within the elevator system. Because the jacket materialcontacts the sheaves, the load upon the cords must be accommodatedbetween the cords and the sheaves by the jacket material.

The compression set characteristic of the jacket material impacts ridequality. In one example, the compression set preferably is about 40%.

Another characteristic of the jacket material that is preferred is ahigh hydrolysis resistance to avoid degradation of the jacket, which mayotherwise occur because of the relatively high temperatures andrelatively high humidity levels commonly experienced within an elevatorhoistway. The material also preferably will not be adversely affected byother contaminants, such as lubricants, that may be encountered in somehoistways. It is also desirable to select a material so that ultravioletradiation resistance is maximized.

The following chart summarizes desired characteristics of the jacketmaterial in one example assembly designed according to this invention.

Property Desired/Preferred Test Methodology Cut tear resistance   ≧50N/mm² ASTM D 624, ISO 34   ≧70 N/mm² Tensile strength   ≧45 N/mm² ASTM D1456, ISO 37 50–60 N/mm² Hydrolysis resistance   ≦55 mm³ ASTM D 5963,ISO 4649 (evaluation per ~40 mm³ (84 days @ 80° C. 95% abrasion loss)Rel. Hum.) Compression set ≦50% ASTM D 395, ISO 815  ~40% (24 hrs @ 70°C.)

Given this description, those skilled in the art will be able to selecta proper jacket material to suit the needs of their particularsituation.

FIG. 3 schematically illustrates a method of making a belt assembly 40designed according to this invention. A cord supply 50 provides thecords 42.

In one example, each cord is pre-made and wound upon an individualspool. An example belt assembly includes twelve individual polymercords.

A positioning device 52 aligns the cords 42 in a desired alignment sothat the cords will extend parallel to a longitudinal axis of the beltassembly 40. The cords are stretched using a load that is selected tocorrespond to a desired percentage of the breaking strength of thecords. The inventive approach includes applying a load that exceeds theanticipated loads when the belt assembly is placed in service in anelevator system. In one example, the cords are prestretched using a loadthat is at least approximately 10% of the breaking strength of thecords. The tension pre-stretching the cords at the 10% of the breakingstrength level is selected in this example because elevator safety codesrequire safety factors typically in the range from 10:1 up to 12:1.Pre-stretching the cords at the 10% level results in belts with littleor no elastic stretch and no construction stretch. In other words, thebelt design typically allows for up to a 10% stretch so that the beltdesign meets safety codes. By pre-stretching at the 10% level, when thebelt is placed in service after being installed in an elevator system,there is essentially no stretch during system operation.

A tensioning device 54 applies the stretching load and controls anamount of tension on the cords 42 during the manufacturing process.Although a single tension station 54 is schematically illustrated,multiple tension devices may be used along the assembly line of the beltassembly 40. For example, the same tension preferably is applied to thecords on both sides of a jacket application station 56. The tensionstation 54 preferably includes a suitably programmed controller thatmonitors and controls the tension within a desired range to pre-stretchthe cord.

Although not specifically illustrated, tension feedback devices (asknown in the art) preferably are incorporated into the manufacturingequipment so that the tension on each individual cord can be monitoredand adjusted as needed throughout the entire assembly process.

The jacket application station 56 preferably includes a suitable mold orother device for applying the jacket material onto the cords 42. Asupply 58 provides the chosen material to the jacket application station56 in a conventional manner. The jacket material may be pressure molded,extruded or otherwise applied to the cords 42. The preloaded cords 42are bonded to the jacket and covered in the urethane material in amanner that prevents any relaxation or unloading of the cords from theprestretched condition.

In one example, rollers 59 are included as part of or immediately afterthe jacket application station 56. The rollers 59 preferably are TEFLON™(polytetrafluoroethylene) coated. The rollers 59 provide a surfacetreatment to the belt assembly immediately after the application of thejacket material. The rollers 59 may provide an embossed pattern on thejacket surfaces, for example. The rollers 59 facilitate dimensionalcontrol of the jacket exterior.

The formed belt assembly 40 preferably is then processed at a finishingstation 60. In one example, the finishing station 60 includes a formingdevice, a dimensional inspection device and a curing cold water bathwhere the jacket material and the cords within the material are cooledto a suitable temperature.

Once cured, the jacket 44 maintains the cords 42 in the prestretchedcondition. Accordingly, the inventive belt assembly has cords that arealready stretched before the belt assembly is installed in an elevatorsystem. The inventive belt assembly experiences little if any elastic orconstruction stretch. The tolerances for how much stretch, if any, isdesired for a given situation can be controlled by controlling the loadapplied to stretch the cords during assembly, for example. Given theselected materials and the particular requirements of a situation, thoseskilled in the art who have the benefit of this description will be ableto control the manufacturing parameters necessary to achieve a desiredlevel of stretch resistance in a finished belt assembly designedaccording to this invention.

The resulting belt assembly 40 preferably is then stored at 62, forexample on spools for shipment to various locations for installation inelevator systems. The belt assembly 40 may be precut to specific lengthsor may be provided in larger quantities where a technician at theinstallation selects the appropriate amount of belt material for aparticular application.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe scope of this invention. The scope of legal protection given to thisinvention can only be determined by studying the following claims.

1. An elevator belt assembly, comprising: a plurality of cords that arestretched to an increased length; and a jacket comprising asubstantially noncompressible urethane over the stretched cords thatkeeps the cords stretched a desired amount without any external loadapplied to the belt assembly.
 2. The assembly of claim 1, wherein thebelt assembly has limited elastic stretch.
 3. The assembly of claim 1,wherein the cords comprise a synthetic material.
 4. The assembly ofclaim 1, wherein the jacket comprises an ether based polyurethane. 5.The assembly of claim 1, wherein the cords are stretched an amountcorresponding to a load that exceeds an anticipated greatest load thatthe assembly will experience once installed in an elevator system. 6.The assembly of claim 1, wherein the cords are stretched an amountcorresponding to a load that is at least approximately 10% of the cordbreaking strength.
 7. An elevator belt assembly made by the process,comprising the steps of: (a) aligning a plurality of cords in a selectedarrangement; (b) stretching the cords by applying a selected amount oftension to increase a length of the cords; and (c) applying a selectedjacket material comprising a substantially noncompressible urethane tothe stretched cords to encase the cords in the jacket; wherein the cordsremain stretched within the jacket without any external load applied tothe belt assembly.
 8. The assembly of claim 7, wherein the cordscomprise a synthetic material.
 9. The assembly of claim 7, wherein thejacket material comprises an ether based polyurethane.
 10. A method ofmaking an elevator belt assembly having a plurality of cords within ajacket, comprising the steps of: (a) aligning the plurality of cords ina selected arrangement; (b) tensioning the cords a selected amount tostretch and increase a length of the cords; and (c) applying a selectedjacket material comprising a substantially noncompressible urethane tothe cords to encase the cords in the jacket so that the cords remainstretched within the jacket wherein the cords are tensioned using a loadthat exceeds an anticipated greatest load that the belt assembly willexperience once installed in an elevator system.
 11. A method of makingan elevator belt assembly having a plurality of cords within a jacket,cormrising the steps of: (a) aligning the plurality of cords in aselected arrangement; (b) tensioning the cords a selected amount tostretch and increase a length of the cords; and (c) applying a selectedjacket material comprising a substantially noncompressible urethane tothe cords to encase the cords in the jacket so that the cords remainstretched within the jacket, wherein the cords are tensioned using aload corresponding to a desired percentage of a breaking strength of thecords, wherein the load corresponds to at least approximately 10% of thecord breaking strength.
 12. The method of claim 10, wherein the jacketmaterial comprises an ether based polyurethane.